1. Field of the Invention
The present invention relates to a rotary head type magnetic recording and reproducing device (hereinafter referred to merely as "a VTR") controlled using control signals superposed on video signals and recorded in video signal tracks on a magnetic tape and, more particularly, to a rotary head type magnetic recording and reproducing device and method in which, when the signal recording operation is temporarily stopped and started again, the recorded patterns are smoothly joined on the magnetic tape, this is, successive picture recording operations are carried out with high accuracy.
2. Description of the Related Art
Heretofore, in order to successively record signals with a VTR, a method has been extremely employed in which a control signal for controlling the forwarding of the magnetic tape is utilized. FIG. 1 illustrates the tape transport system of a VTR in which a control signal recorded on the control track is utilized for controlling the transport of a magnetic tape. The magnetic tape 1 is pushed against the capstan shaft 43 by the pinch roller 44, and is transported by rotation of the capstan shaft 43 past the audio head 6. In a normal recording or reproducing mode, the magnetic tape 1 is supplied from a supply reel 40, wound on drum 42 having a rotary drum video head 24 after passing over tension arm 41 and overall width erasing head 31. After passing over the audio head 6 and the capstan shaft 43, the tape is wound on the take-up reel 46.
FIG. 2 illustrates a recording pattern on a magnetic tape having control tracks in addition to video signal tracks that are formed by a helical scan type VTR. In this case, on the magnetic tape 1, a video signal track 2 is generally recorded obliquely, and control signals 3 are recorded at predetermined intervals in the tape running direction. The control signals 3 are used to control the tape transport operation, that is, the control signals are used to scan the video signal rotary magnetic head 24 over the video tracks 2 accurately during playback. In the following description, a control signal to be recorded on the magnetic tape 1 will be referred to as a "recording control signal", a control signal actually recorded on the magnetic tape will be referred to as a "control signal", and a control signal reproduced from the magnetic tape will be referred to as a "reproduced control signal".
In general, the control signal 3 is formed on the tape by subjecting the vertical synchronizing signal of a video signal to a be recorded to 1/2 frequency division. The transport of the magnetic tape 1 is controlled so that the time that the control head 6 detects the control signal coincides with the time the video signal rotary magnetic head 25 reaches the start point of the video signal track 2, i.e., the portion where the vertical synchronizing signal is recorded.
If the tape 1 is temporarily stopped during recording, and the tape 1 is run again to immediately restart the recording operation, then on the portion of the tape which corresponds to the joining of the two successive recording operations (hereinafter referred to as the "signal joining portion"), the video signal track 2 varies in recording phase or inclination angle. Accordingly, the picture reproduced from this portion is irregular. When the magnetic tape 1 is temporarily stopped, the locus of the video signal rotary head 24 is as indicated by the broken lines 4 in FIG. 2. To prevent the above-described problem, the following operation is carried out in the servo control system.
When a temporary stop instruction is initiated during picture recording, the picture recording operation is stopped immediately, and the magnetic tape 1 is rewound a predetermined length in the opposite direction. After rewinding, the magnetic tape 1 is stopped and the VTR is ready for the next recording operation.
When the temporary stop instruction is deactivated, the magnetic tape 1 is run in the forward direction. In this situation, the recording operation is not restarted immediately. After the reproduced control signal from the control track of the magnetic tape 1 is synchronized with the vertical synchronizing signal of a new video signal, that is, after the phase of the video signal track recorded previously coincides with that of a new video signal track to be recorded, the recording mode is initiated to restart the recording operation again. In this way, a successive picture recording operation is carried out so that the previously recorded picture is joined smoothly with a new picture to be recorded.
However, the above-described method suffers from a problem when the rotary magnetic head's locus on the magnetic tape, at the time the recording operation is started, the magnetic tape is being transported in the forward direction in the recording mode after removal of the temporary stop instruction, is shifted, in the tape running direction, with respect to the rotary magnetic head's locus on the magnetic tape when the recording operation is stopped by the temporary stop instruction. That is, if the locus is shifted forward on the tape, a new recording pattern overlaps the recording pattern formed on the magnetic tape before removal of the temporary stop instruction. If the locus is shifted backward on the tape, an unrecorded portion or gap is formed on the magnetic tape. During the playback of a magnetic tape recorded using this technique, the reproduced picture is visually unacceptable.
In order to overcome the locus shifting problem, the magnetic tape is run in the reverse direction after the recording operation is stopped when reception of the temporary stop instruction. The number of control signals reproduced from the control track for the period during which the tape is run in the reverse direction are counted and stored. After removal of the temporary stop signal, control signals are reproduced from the control track and counted. The number of control signals thus counted is compared with the number of control signals stored. The recording operation is started when the numbers are equal.
In the above-described conventional VTR, contract between the control head and the magnetic tape is sometimes insufficient when the tape is stopped and then started, or when the tape is run in the reverse direction. Therefore, unless the mechanical accuracy is high, reproduction of the control signals is unreliable during the above-described transition time of the tape running operation. As a result the picture overlap period is increased, or the unrecorded gap is formed. With either result, the reproduced picture is visually unacceptable.
A VTR of the type in which tracking pilot signals are recorded with a rotary head as it performs successive picture recording operations is disclosed in, for example, Japanese patent application Laid-Open No. 203658/1983. That is, upon reception of a temporary stop instruction, the recording operation is temporarily stopped with the recording of signals on a track corresponding to a predetermined pilot signal. Thereafter, similar to the above-described situation, the tape is transported or rewound a predetermined length to be ready for the next recording operation. After removal of the temporary stop instruction, the pilot signal is reproduced to effect tracking servo control. The last recorded track is detected to allow the recording operation to start again from the last track. In order to detect the last track, cross-talk between the pilot signals of adjacent tracks is utilized. However, when the reproducing mode is started after elimination of the temporary stop instruction, the cross-talk cannot be detected for a predetermined period of time. In other words, cross-talk cannot be detected before the tracking servo control is accomplished. Accordingly, it is difficult to detect the last track. A method of detecting the track next to the last track from the presence or absence of the pilot signal in the track is also disclosed. However, the method is disadvantageous in that, even if the recording operation is started again immediately when the last track is detected, an unrecorded gap is formed on the tape.